The present invention relates to compositions based on polyolefins and on low-melting-point polyamides and more particularly to compositions containing a polyamide matrix and comprising a polyolefin dispersed phase. They consist of, for example, PA-6/6,6, polyethylene or polypropylene and usually a compatiblizer which is, for example, a functionalized polyolefin. These compositions are useful for moulding articles or for making films used, for example, in packaging.
Compositions based on PA-6 and polyolefins, known elsewhere as being excellent barrier materials (with respect to CH3Br, styrene, pentane, etc.), are processed, by. tubular blown-film extrusion for example, at temperatures of the order of 260xc2x0 C. These temperatures are not compatible with coextruded structures in which at least one of the layers has a certain heat sensitivity such as a layer of ethylene-vinyl acetate (EVA) copolymers. In addition, these high temperatures cause processing problems for coextruded structures in the presence of PE (polyethylene) layers.
Moreover, films consisting of these compositions based on PA-6 and PE exhibit low tear strength in the longitudinal direction. Consequently, the invention proposes novel barrier films exhibiting improved tear strength, these being obtained within the context of a monolayer or multilayer construction containing at least one layer of an alloy of the low-melting-point polyamide/polyolefin type which can be processed, in tubular blown-film coextrusion, at low enough temperatures for them to be compatible with layers of heat-sensitive polymers.
The prior art has not disclosed this technical problem. Patent EP 766,913 discloses a film consisting of a blend comprising at least one polyamide and at least one polyolefin, the said film being laid out over an agricultural soil into which a fumigant is injected. Soil treatment by fumigation consists in injecting gases into the soil, before sowing or planting, in order to disinfect the earth, and then the soil is covered with a film of a plastic in order to retain these gases in the soil and thus allow them to act. It is possible, for example, to use methyl bromide, 1,3-dichloropropene, methyl chloride, 3,5-dimethyltetrahydro-1,3,5-thiadiazin-2-thione, sodium tetrathiocarbonate or metham sodium (CH3NHCS.S Na).
According to a first embodiment, this prior art also relates to a film comprising the above layer and a layer essentially consisting of a polyolefin. According to a second embodiment, this prior art also relates to a film comprising the previous layer arranged between two layers of polyolefin. The technical problem of the present invention was not mentioned; the polyamide used was still PA-6.
Patent EP 807,519 relates to a multilayer film, useful for making flexible sachets, comprising (i) a barrier film based on a polyamide/polyolefin blend and (ii) on at least one of its sides, a film based on a high-frequency weldable ethylene-unsaturated ester copolymer. It is useful for making flexible sachets of detergents, bleach or fabric softeners. The examples describe barrier films consisting of PA-6 and polyethylene and weldable EVA films. As in the previous prior art, the technical problem of the present invention was not mentioned and the polyamide used was still PA-6.
It has now been discovered that compositions based on polyolefins and low-melting-point polyamides can be produced which can be converted into films and can be coextruded with other polymers in order to make multilayer structures.
The invention therefore relates to compositions containing a polyamide matrix (A) and a polyolefin dispersed phase (B), in which compositions the polyamide has a melting point below that of PA-6 and the dispersed phase consists of at least one polyolefin (B) chosen from functionalized polyolefins (B1) and non-functionalized polyolefins (B2).
The present invention therefore relates to films consisting of the above compositions.
The films of the present invention have many advantages: they are processed at low temperature, they have a high tear strength and they exhibit a barrier nature.
Advantageously, the films of the invention may be processed at lower temperatures than alloys of the prior art based on PA-6 (melting point=223xc2x0 C.), the tubular blown-film coextrusion of which is normally carried out at 260xc2x0 C. A reduction of at least 20 to 30xc2x0 C. is expected. This characteristic is most particularly beneficial in the field of multilayer film coextrusion in which the outer layers consist of PE (better bubble strength because of the higher viscosity of the PE layers) or of heat-sensitive copolymers of ethylene and polar monomers (for example, EVA). Thus, the thermal degradation of the external layers is limited.
Monolayer or multilayer films containing at least one layer according to the present invention exhibit improved tear strength in the longitudinal direction compared with constructions known to those skilled in the art, such as those described in EP 766,913. Compared with these PE-based films, the films according to the present invention possess lower permeabilities with respect to the following agents: CH3Br, O2 and CO2.
The expression xe2x80x9clow-melting-point polyamidexe2x80x9d should be understood to mean any polyamide whose melting point is less than 220xc2x0 C. These are often copolyamides. Mention may be made of the copolyamides resulting from the condensation of at least two alpha,omega-aminocarboxylic acids or of two lactams, or of a lactam with an alpha,omega-aminocarboxylic acid. Mention may also be made of the copolyamides resulting from the condensation of at least one alpha,omega-aminocarboxylic acid (or a lactam) with at least one diamine and at least one dicarboxylic acid.
By way of examples of lactams, mention may be made of those having from 3 to 12 carbon atoms in the main ring, these being possibly substituted. Mention may be made, for example, of xcex2,xcex2-dimethylpropiolactam, xcex1,xcex1-dimethylpropiolactam, amylolactam, caprolactam, capryllactam and lauryllactam.
By way of examples of alpha,omega-aminocarboxylic acids, mention may be made of aminoundecanoic acid and aminododecanoic acid. By way of examples of dicarboxylic acids, mention may be made of adipic acid, sebacic acid, isophthalic acid, butanedioic acid, 1,4-cyclohexyldicarboxylic acid, terephthalic acid, the sodium or lithium salt of sulphoisophthalic acid, dimerized fatty acids (these dimerized fatty acids have a dimer content of at least 98% and are preferably hydrogenated) and dodecanedioic acid HOOCxe2x80x94(CH2)10xe2x80x94COOH.
The diamine may be an aliphatic diamine having from 6 to 12 carbon atomsxe2x80x94it may be an aryl diamine and/or a saturated cyclic diamine. By way of examples, mention may be made of hexamethylenediamine, piperazine, tetramethylenediamine, octamethylenediamine, decamethylenediamine, dodecamethylenediamine, 1,5-diaminohexane, 2,2,4-trimethyl-1,6-diaminohexane, diamine polyols, isophorone diamine (IPD), methylpentamethylenediamine (MPDM), bis(aminocyclohexyl)-methane (BACM) and bis(3-methyl-4-aminocyclohexyl)methane (BMACM).
The expression xe2x80x9clow-melting-point polyamidexe2x80x9d should also be understood to mean any amorphous polyamide having no melting point.
By way of examples of polyamides (A), mention may be made of caprolactam/lauryllactam copolymers (PA-6/12), caprolactam/hexamethylenediamine, adipic acid copolymers (PA-6/6,6), caprolactam/lauryllactam/hexamethylenediamine, adipic acid copolymers (PA-6/12/6,6), caprolactam/hexamethylenediamine, azelaic acid/11-aminoundecanoic acid/lauryllactam copolymers (PA-6/6,9/11/12), caprolactam/hexamethylenediamine, adipic acid/11-aminoundecanoic acid/lauryllactam copolymers (PA-6/6,6/11/12) and hexamethylenediamine, azelaic acid/lauryllactam copolymers (PA-6,9/12).
Advantageously, (A) is chosen from PA-6/12 and PA-6/6,6.
A non-functionalized polyolefin (B2) is conventionally a homopolymer or copolymer of alpha-olefins or of diolefins, such as, for example, ethylene, propylene, 1-butene, 1-octene and butadiene.
By way of examples, mention may be made of:
homopolymers such as polyethylene, particularly LDPE, HDPE, LLDPE or VLDPE, metallocene polyethylene, or polypropylene;
ethylene/alpha-olefin copolymers such as ethylene/propylene copolymers or EPRS;
styrene/ethylene-butylene/styrene block copolymers (SEBS), styrene/butadiene/styrene block copolymers (SBS), styrene/isoprene/styrene block copolymers (SIS), styrene/ethylene-propylene/styrene block copolymers (SEPS) and ethylene/propylene/diene monomer copolymers (EPDM);
copolymers of ethylene with at least one product chosen from salts or esters of unsaturated carboxylic acids such as alkyl (meth)acrylates (for example, methyl acrylate), or vinyl esters of saturated carboxylic acids such as vinyl acetate, the proportion of comonomer possibly being as much as 40% by weight.
The functionalized polyolefin (B1) may be an alpha-olefin polymer having reactive units (the functional groups); such reactive units are acid, anhydride or epoxy functional groups. By way of example, mention may be made of the above polyolefins (B2) which are grafted or are copolymerized or terpolymerized by unsaturated epoxides such as glycidyl (meth)acrylate, or by carboxylic acids or the corresponding salts or esters, such as (meth)acrylic acid (this possibly being completely or partially neutralized by metals such as Zn, etc.) or else by carboxylic acid anhydrides such as maleic anhydride. A functionalized polyolefin is, for example, a PE/EPR blend, the weight ratio of which may vary between wide limits, for example between 40/60 and 90/10, the said blend being cografted with an anhydride, especially maleic anhydride, with a degree of grafting, for example, of 0.01 to 5% by weight.
The functionalized polyolefin (B1) may be chosen from the following (co)polymers, grafted with maleic anhydride or glycidyl methacrylate, in which the degree of grafting is, for example, from 0.01 to 5% by weight:
PE, PP, copolymers of ethylene with propylene, butene, hexene, or octene and containing, for example, from 35 to 80% by weight of ethylene;
ethylene-vinyl acetate copolymers (EVA), containing up to 40% by weight of vinyl acetate;
ethylene-alkyl (meth)acrylate copolymers, containing up to 40% by weight of alkyl (meth)acrylate;
ethylene-vinyl acetate (EVA)-alkyl (meth)acrylate copolymers, containing up to 40% by weight of comonomers.
The functionalized polyolefin (B1) may also be chosen from ethylene/propylene copolymers containing predominantly propylene, these being grafted by, maleic anhydride and then condensed with a monoaminated polyamide (or polyamide oligomer) (products described in EP-A-0,342,066).
The functionalized polyolefin (B1) may also be a copolymer or terpolymer of at least the following units: (1) ethylene, (2) an alkyl (meth)acrylate or a vinyl ester of a saturated carboxylic acid and (3) an anhydride such as maleic anhydride or a (meth)acrylic acid or an epoxy such as glycidyl (meth)acrylate.
By way of examples of functionalized polyolefins of this latter type, mention may be made of the following copolymers, in which the ethylene preferably represents at least 60% by weight and in which the termonomer (the functional group) represents, for example, from 0.1 to 10% by weight of the copolymer:
ethylene/alkyl (meth)acrylate/(meth)acrylic acid or maleic anhydride or glycidyi methacrylate copolymers;
ethylene/vinyl acetate/maleic anhydride or glycidyl methacrylate copolymers;
ethylene/vinyl acetate or alkyl (meth)acrylate/(meth)acrylic acid or maleic anhydride or glycidyl methacrylate copolymers.
In the above copolymers, the (methyacrylic-acid may be salified with Zn or Li.
The term xe2x80x9calkyl (meth)acrylatexe2x80x9d in (B1) or (B2) denotes C1 to C8 alkyl methacrylates and acrylates, and may be chosen from methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate and ethyl methacrylate.
Moreover, the aforementioned polyolefins (B1) may also be crosslinked by any suitable process or agent (diepoxy, diacid, peroxide, etc.); the term functionalized polyolefin also includes blends of the aforementioned polyolefins with a difunctional reactive agent such as a diacid, dianhydride, diepoxy, etc., which is capable of reacting with them.
The copolymers mentioned above, (B1) and (B2), may be copolymerized so as to form random or block copolymers and may have a linear or branched structure.
The molecular weight, the MFI index and the density of the polyolefins may also vary over a wide range, as those skilled in the art will appreciate. MFI is the abbreviation for Melt Flow Index. It is measured according to the ASTM 1238 standard.
Advantageously, the non-functionalized polyolefins (B2) are chosen from any ethylene homopolymer or copolymer of ethylene and a higher comonomer, such as butene, hexene, octene or 4-methyl-1-pentene. Mention may be made, for example, of high-density PE, medium-density PE, linear low-density PE, low-density PE and very low-density PE. These polymers are known to those skilled in the art as being produced by a xe2x80x9cradicalxe2x80x9d process, by xe2x80x9cZieglerxe2x80x9d -type catalysis or, more recently, by so-called xe2x80x9cmetallocenexe2x80x9d catalysis.
Advantageously, the functionalized polyolefins (B1) are chosen from any polymer comprising alpha-olefin units and units carrying polar reactive functional groups such as epoxy, carboxylic acid or carboxylic acid anhydride functional groups. By way of examples of such polymers, mention may be made of ethylene/alkyl acrylatelmaleic anhydride terpolymers or ethylene/alkyl acrylate/glycidyl methacrylate terpolymers, such as Lotader(copyright) polymers, or maleic-anhydride-grafted polyolefins such as the Orevac(copyright) polymers, as well as ethylene/alkyl acrylate/(meth)acrylic acid terpolymers.
The MFI of (A) and the MFIs of (B1) and (B2) may be chosen within a wide range; however, it is recommended, in order to facilitate the dispersion of (B) in the matrix (A), that the MFI of (A) be greater than that of (B).
Advantageously, the proportion of (A) is from 50 to 90 parts (by weight) per 50 to 10 parts of (B). For lower proportions of (B), for example 10 to 15 parts, it suffices to use a non-functionalized polyolefin (B2). The proportion of (B2) and (B1) in the dispersed phase (B) depends on the amount of functional groups present in (B1) as well as on their reactivity. Advantageously, 5 to 15 parts of (B1) per 30 to 20 parts of (B2), respectively, are used.
The compositions according to the invention may furthermore contain at least one additive chosen from:
fillers (mineral fillers, fire retardants, etc.);
fibres;
dyes;
pigments;
brighteners;
antioxidants;
UV stabilizers.
The compositions of the invention are manufactured by melt blending of the constituents (A) and (B) using the standard techniques for thermoplastics. Mixers, extruders or kneaders may be used. The films are manufactured either by the blow extrusion of a tubular film or by extrusion casting.
The present invention also relates to multilayer structures comprising the above film and at least one film of a heat-sensitive polymer. The latter may be, for example, an EVA, an ethylene/alkyl (meth)acrylate copolymer or a polyethylene. These structures are manufactured by tubular blown-film coextrusion or coextrusion casting.
The films of the invention, which are monolayers or multilayers, are useful for items of packaging; for the packaging of polyesters to be crosslinked using the SMC technique as described in EP 786,319; for fumigation, as described in EP 766,913; for the packaging of detergents, bleaches or fabric softeners, as described in EP 807,519; and for the packaging of expanded polystyrene beads, as described in EP 907,508.